Aluminum is used extensively in the semiconductor industry to provide interconnections on integrated circuits. Devices which utilize aluminum interconnections are generally heated to about 450.degree. C. in an inert atmosphere to cause silicon to dissolve into the aluminum, while also dissolving any silicon dioxide (SiO.sub.2) at the aluminum-silicon interface, thereby to insure good ohmic contact between the aluminum and the silicon. As aluminum does not dissolve uniformly over the entire contact area, "alloy spiking" results. The term "alloy spiking" means that alloys of silicon and aluminum form pits in the silicon surface which sometimes penetrate to the underlying PN junction, shorting the junction and making the circuit inoperative.
The amount of silicon which dissolves into the aluminum film, and consequently, the amount of "alloy spiking", is determined by the solid solubility of silicon in aluminum at any given temperature. For example, only about 0.6% silicon will dissolve into aluminum at 450.degree. C. In order to prevent "alloy spiking" while insuring good bonding, aluminum films containing controlled amounts of silicon, exceeding the solid solubility limit, are deposited. Therefore, when the alloy step, i.e. the heating step, is performed, excessive, "alloy spiking" will not result. Unfortunately, the presence of silicon in the aluminum films makes the aluminum harder, so it becomes difficult to bond wires to the contact pads.
In addition, silicon precipitates out of the aluminum-silicon solution non-uniformly during cooling. As a result, bonding problems occur when the silicon precipitates out of the solution at the top of the aluminum film. The higher the percentage of silicon in the top surface, the more difficult it is to have good wire bonds to that surface.
Heretofore it has not been possible to determine whether the presence of silicon in the aluminum layer has been the cause of poor wire bonding in specific situations.